Conventionally, a transfer method adopting an optical fiber system has been spreading. An optical fiber cable which is used in such an optical transmission has been widely used for information instrument, CATV, broadcasting equipment, an optical measuring device, LAN equipment and the like.
An optical plug is mounted on an end portion of the optical fiber cable. The optical plug includes, for example, an optical fiber holding member, a caulking seat, a compression coil spring, a stopper ring and a plug frame (see Japanese Unexamined Patent Publication 2001-141960, for example). On an inner wall surface of a caulking ring, a female-thread-like projections are formed, for example.
According to the optical plug, the optical fiber cable is inserted into the inside of the caulking seat and, at the same time, high tensile strength wires (for example, aramid fibers) are arranged outside the caulking seat. Thereafter, by caulking the caulking seat with the caulking ring from the outside, the high tensile strength wires can be clamped between the caulking seat and the caulking ring. As a result, the high tensile strength wires are firmly held by the caulking seat and the caulking ring.
However, the above-mentioned optical plug, since the female threads are formed in the inner wall surface of the caulking ring, it is difficult to achieve the further miniaturization of the optical plug.
To overcome the above-mentioned drawbacks, there has been proposed a method in which an annular groove is formed in an outer periphery of the caulking seat, thus forming depressions and projections, and at the same time, an annular projection is formed on the caulking ring, and the annular projection is fitted into the annular groove formed in the caulking seat.
However, according to the method, it is necessary to form the annular projection in a die which presses the caulking ring. Accordingly, a height of the projection from a bottom surface is 0.3 mm, for example, and hence, it is necessary to machine the dies with extreme accuracy, thus pushing up cost.